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Right choice is (b) False

To ELABORATE: The surface irregularities of the solidifying casting results in irregular contacts to establish between the die wall and the casting PRODUCED. This always results in a temperature drop across the interface. The extent of temperature drop or the degree of resistance mainly DEPENDS on the contact area, physical and thermal properties of the materials in contact.

Correct choice is (b) False

Explanation: During the solidification of casting in an insulating mould, the casting made is generally of ductile nature as the heat transfer to the SURROUNDING is restricted and the casting is kept for LONG TIME in the mould which have slow solidification rate that causes coarse grain STRUCTURE in the casting PRODUCED.

Correct choice is (a) True

The explanation: In SOLIDIFICATION of casting material, it is COMMONLY starts from the centre-line of the mould before the solidification is complete even at the mould FACE. In the chilled mould, due to the RAPID HEAT extraction from the casting, a narrow like liquid-solid zone sweeps across the molten metal.

The CORRECT answer is (a) True

For EXPLANATION: The solidification process STARTS in the mould with the secondary cooling zone using a combination of water spray and radiation cooling, which maintains high heat flux. Solidification speciality of this technology ARISES from the DYNAMIC nature of the casting process which relates to handling of very high heat flux in the mould.

The correct OPTION is (a) True

The explanation: In the process of casting different materials, due to complexities of material behavior, internal liquid metal pressure and the mould geometry MAKE the CALCULATION more difficult to obtain the AIR GAP at the interface. To solve this, proper care is to take during the process of casting products.

Correct answer is (b) False

Best explanation: For no contact RESISTANCE between the metal and mould, the solidification process is CONSIDERED by assuming that the thermal resistance at the INTERFACE is of over-riding IMPORTANCE. In this KIND of cases, superheating is not considered for the temperature distribution in the casting solidification.

The correct choice is (a) Less than 1

The explanation is: CHILL mould castings use a massive metal mould with a large THERMAL capacity or water cooled metal mould, so that biot number (BI) is always less than 1. When the melt is poured in at a temperature above its melting temperature (Tm), it first COOLS and then begins solidification when T = Tm.

Right answer is (b) False

Best EXPLANATION: The mould is a cavity where liquid metal is poured to solidify and FORM the desired shape of the casting. The rate at which castings solidify affects its microstructure, quality, and MECHANICAL PROPERTIES. Basically, the casting which cools quickly will have a FINE grain structure and which cools very slowly will have a coarse grain structure.

Right OPTION is (a) True

To elaborate: In CASTING system, riser is provided to compensate the liquid and solidification shrinkage during solidification of the casting in the mould. But to feed the melt at desired LOCATIONS within the casting, it is very important to IDENTIFY the correct location on the casting system to set up the riser mechanism.

The correct answer is (a) True

To elaborate: During SOLIDIFICATION of casting, the SUCCESSIVE droplet’s interface has lower temperature gradient when compared to the temperature gradient experienced by the FIRST droplet of the material. Thus, heat transfer occurs at low rates and successive droplets take longer TIME to solidify that the first droplet of the casting material.

Correct CHOICE is (a) True

Easiest explanation: For the CASTING line productivity and to increase casting speed, rapid cooling of strand surfaces must be EMPLOYED. It results in the development of THERMAL stresses and formation of surface cracks if the casting speed and cooling CONDITIONS or the arc of casting system are not appropriate for the casting process.

Correct answer is (a) True

For explanation: During the solidification of casting MATERIAL in the mould, concave, convex and PLANE types of METAL mould interfaces are mainly considered for the estimation of freezing time of molten metal. These types of interface show the DIFFERENT direction of heat TRANSFER from the casting material to the mould.

Correct choice is (a) True

To explain: The mould material used should be of high REFRACTORINESS because the mould used for the solidification of casting is to be INSULATED. So the mould should be capable of MAINTAINING all the thermal resistance to withstand very high temperature for the long duration of time until the casting is MADE.

The correct ANSWER is (b) False

Explanation: There is very little segregation ahead of dendrite tip because the main partitioning is of solute trapped between the dendrite side ARMS. The scale of this segregation can be decreased by increasing the SOLIDIFICATION rate because the dendrite arm SPACING then decreases. Segregation can also be decreased by inducing a greater number density of nuclei.

Correct answer is (d) 600 – 700

The explanation: As the FIRST droplet solidified when the successive droplets MAKE an impact to it and the temperature of the pre-solidified droplet is very close to its melting temperature. The droplet temperature is approximately greater or equals to 623 K, at which the pre-solidified droplet re-melts and SHOWS re-melting behaviour at different time INSTANTS.

Correct answer is (a) True

For explanation I would say: To have PROPER directional solidification and to maintain the RISER mechanism, the chill USED should be placed at the ends of the riser. When more than one riser is used in the casting SYSTEM then the chill should be placed at the midway between the TWO risers to have accurate and systematic solidification.

Right CHOICE is (b) False

The explanation is: The increase in MOULD thickness can increase the rate of solidification of casting material. This is because the increase in thickness increases the amount of HEAT ABSORBED by mould or due to the chilling effect of the mould which is ALSO dependent on the heat content of the molten metal.

Right answer is (a) True

For explanation I would SAY: It is an essential FEATURE of CHILLED castings that the surface temperature is appreciably lower than the melting point of the molten metal, which totally differs from the sand castings and it moderates to steep the temperature gradient exists in the solid metal or CASTING produced.

Right answer is (b) False

The explanation: The difference in the PROGRESS of crystallization at the different points in the CASTING material does not make fast growth of crystals, even this makes the hampering of CRYSTAL growth which basically restricts or retards the columnar growth of crystals starting from the MOULDING surface during casting process.

Correct choice is (a) True

Explanation: GOOD THERMAL conductivity of the solidified METAL can provide considerable thermal resistance. Because of this, the SURFACE temperature of the casting material can be lower down below than the freezing temperature of the casting, which results in the formation of sub-cooled solidified casting.

Correct answer is (d) Thermal resistance

To EXPLAIN: In the casting PROCESS, the heat flow is generally controlled by the thermal resistance of the metal-MOULD interface. These interfaces can be of convex, concave or plane shape, depending on the heat flow rate required for the casting. These processes mainly INCLUDE PERMANENT mould casting and die casting.

Right answer is (a) True

To elaborate: The amount of heat that should be removed from CASTING to make it solidify is directly proportional to the amount of superheating and ALSO to the amount of metal present in the casting or the casting volume. CONVERSELY, the ability to remove heat from casting is directly proportional to the amount of exposed surface area of the casting.

Right choice is (b) False

The best I can explain: Grey cast iron is an interesting EXCEPTION where SOLIDIFICATION occurs in TWO STAGES. The shrinkage associated with the first stage can be compensated by the expansion of the casting DUE to the presence of graphite flakes in the material. Due to this, there is no use of riser in the casting system.

Correct ANSWER is (a) True

The EXPLANATION is: Solidification of metal in the continuous casting line proceeds under non-equilibrium conditions and is specified by the large cooling rate. These can lead to the OCCURRENCE of DEFECTS at cast strands such as surface or internal cracks, which might also affect the composition of the casting material.

The correct option is (b) False

Explanation: Chvorinov’s rule is not USED for the aspect of finishing of the casting. It is mainly used to ensure that the casting made in the MOULD will SOLIDIFY before the riser. This is very necessary if the LIQUID metal within the riser is to effectively feed the casting to compensate for SOLIDIFICATION shrinkage.

Correct option is (c) Chills

Explanation: To avoid the problem of difference in progress of crystallization, a LARGE thermal gradient within the MOULD can be produced by having chills in the casting system. Chills GENERALLY are cooled metal block with the HIGH thermal conductivity; this is normally PLACED at the mould’s end.

The correct answer is (a) True

For explanation I would say: The friction concept is very useful in EXPLAINING the INCREASED tendency of breakout with the increase in casting speed. Analysis of friction at the interface of MOULD and casting is done to specify the speed of the casting process or it can also be adjusted by maintaining the AMOUNT of LUBRICATION at the gap.

Correct choice is (d) fs = ηs*H

For explanation: When the relative MOVEMENT occurs between the casting and the solidified mould slag, then the friction force is generated by the solid-solid contact. The RESULTING solid friction (fs) is EXPRESSED as fs = ηs*H, where ηs is the COEFFICIENT of solid friction, and H is the Ferro-static PRESSURE of molten metal.